Combined effects of blowing ratio and mist diameter with mainstream turbulence intensity in mist-assisted film cooling

Abstract

Advanced cooling techniques are essential in modern gas turbines to improve the efficiency of the Brayton cycle by raising the turbine inlet temperature. Mist-assisted film cooling offers an innovative solution for cooling high-temperature gas turbine blades. When mist particles with various momenta are injected through the cooling holes, the interplay between mainstream turbulence intensity (Tu) and mist momentum plays a crucial role in mist-assisted film cooling under high Tu conditions. Hence, this numerical study investigates the relationship between mainstream Tu and mist characteristics for the first time, considering the blowing ratio and mist diameter as controlling parameters. Film effectiveness and particle distribution statistics are analysed to understand their correlation. The results demonstrate that mist-assisted film effectiveness follows the trend of air-only film cooling with varying blowing ratios and Tu; however, the magnitude is amplified. The influence of the mist diameter on film effectiveness is determined by the surface-area-to-volume ratio and Stokes number. These factors impact the sensitivity of particles to Tu and subsequently affect film effectiveness. This study provides a novel quantitative analysis of the combined effect of mainstream Tu and mist on film cooling effectiveness, revealing the correlation between mist and mainstream parameters.

Highlights

• Combined effect of mainstream turbulence intensity (Tu) and mist characteristics is investigated.

• High mainstream Tu significantly increases the cooling enhancement induced by mist.

• Mist-assisted film cooling exhibits similar trends to varying mainstream Tu and blowing ratio.

• Mist diameter significantly influences the response to Tu, governed by surface-area-to-volume ratio and Stokes number.

• Small particles demonstrate the highest cooling effectiveness and variation by Tu.

KEYWORDS:

• Gas turbine
• film cooling
• film cooling effectiveness
• mist-assisted film cooling
• Mainstream turbulence

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported in part by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government (MOTIE) (20193310100060, Evaluation of the performance for F-class or more gas turbine blade prototypes). This research was also supported by the Korea Electric Power Corporation (Grant number: R21XO01-26) and Chung-Ang University Graduate Research Scholarship in 2022.